A measuring device of this type is known from DE 38 14 634 A1, U.S. Pat. Nos. 4,252,124 and 4,218,299.
Such measuring devices are used, for example, to measure the pH of foods such as meat. Usually a chamber is formed between the first electrode and the casing, with a second electrode, usually a gel, accommodated in the chamber. The two electrodes are connected to an analyzer circuit for determining the pH of a liquid of the material to be measured that has penetrated between the electrodes.
First electrodes for pH measurement are usually made of glass or have glass as a casing. For the measurement, the measuring device together with the glass electrode is driven into the material to be measured with great force. The electrode is then subjected to a substantial mechanical stress in the axial direction, i.e., the direction of penetration, e.g., due to the electrode striking a bone. Because of the brittleness of glass, these glass electrodes are able to withstand only a minimal stress, which may often result in breakage, e.g., when they become tilted, during penetration or extraction of the glass electrode or if it is dropped.
To avoid this problem, there are known measuring devices in which the glass electrode and/or the gel surrounding the glass electrode is first enclosed by a glass casing and then by a metal or plastic shell. Although this slightly improves the load-bearing capacity of the glass electrode perpendicular to the axial direction, even the slightest bending of the casing, which is transferred directly to the glass electrode, however, still results in breakage of the glass electrode and/or the glass shell surrounding the electrode.
Because of this double casing of glass and plastic, the measuring device has a disadvantageous thickness in the area of the tip of the probe, so that large holes are produced in the material to be measured by performing the measurement. Furthermore, such measuring devices having thick measuring probes are not suitable for measurements in containers having small insertion openings such as bottles, test tubes and the like.
DE 100 04 583 A1 describes another measuring device of this species having a penetrating electrode. To prevent breakage of the glass electrode, the elongated glass electrode is mounted so that it is pivotable. Therefore the glass electrode may yield to this load to a certain extent in the case of a transverse load perpendicular to its axial direction, so that breakage of the glass electrode is usually prevented in this case. It remains problematical if the glass electrode is additionally or exclusively subjected to a force in the axial direction of the glass electrode, e.g., when it directly strikes a hard bone or drops to the floor. In this case, there is still the risk of breakage of the glass.
Accordingly, it is desirable to provide a measuring device which is designed to be sturdier with respect to loads in the axial direction of the penetrating electrode. Furthermore, a method and an application are also described.